Coupling aperiodic channel state information (CSI) reference signal (RS) (CSI-RS) structure with feedback content and reporting timing

ABSTRACT

Certain aspects of the present disclosure provide techniques for coupling a structure in which aperiodic channel state information reference symbols (CSI-RSs) are received with the content and timing of channel feedback. An example method generally includes receiving a request for channel feedback identifying a type of channel feedback to be provided to the BS and a type of CSI-RS to be used for generating the identified type of channel feedback, transmitting an indication of an amount of time used to generate the identified type of feedback based on the identified type of CSI-RS, receiving a triggering signal indicating at least a location of one or more CSI-RSs and a time at which the UE is to report the channel feedback, receiving the one or more CSI-RSs in the indicated location, generating the channel feedback based on the one or more CSI-RSs, and transmitting the generated feedback to the BS.

This application is a national stage application under 35 U.S.C. 371 ofPCT/CN2017/072896, filed Feb. 4, 2017, which is assigned to the assigneeof the present application and is expressly incorporated by reference inits entirety.

BACKGROUND Field of the Disclosure

Aspects of the present disclosure relate generally to wirelesscommunications systems, and more particularly, to aperiodic channelstate information (CSI) reference symbol (RS) (CSI-RS) structures withthe content and timing of channel feedback reports.

Description of Related Art

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includeLong Term Evolution (LTE) systems, code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

In some examples, a wireless multiple-access communication system mayinclude a number of base stations, each simultaneously supportingcommunication for multiple communication devices, otherwise known asuser equipment (UEs). In LTE or LTE-A network, a set of one or more basestations may define an e NodeB (eNB). In other examples (e.g., in a nextgeneration or 5G network), a wireless multiple access communicationsystem may include a number of distributed units (DUs) (e.g., edge units(EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs),transmission reception points (TRPs), etc.) in communication with anumber of central units (CUs) (e.g., central nodes (CNs), access nodecontrollers (ANCs), etc.), where a set of one or more distributed units,in communication with a central unit, may define an access node (e.g., anew radio base station (NR BS), a new radio node-B (NR NB), a networknode, 5G NB, gNB, etc.). A base station or DU may communicate with a setof UEs on downlink channels (e.g., for transmissions from a base stationor to a UE) and uplink channels (e.g., for transmissions from a UE to abase station or distributed unit).

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is new radio (NR), for example, 5G radioaccess. NR is a set of enhancements to the LTE mobile standardpromulgated by Third Generation Partnership Project (3GPP). It isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingOFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink(UL) as well as support beamforming, multiple-input multiple-output(MEMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR technology.Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

BRIEF SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedcommunications between access points and stations in a wireless network.

Certain aspects of the present disclosure generally relate to methodsand apparatus for coupling an aperiodic channel state informationreference symbol (CSI-RS) structure with the content and timing ofchannel feedback. As described herein, UEs can inform a base station(e.g., a gNodeB) of timing information associated with calculating andreporting a requested type of channel feedback, and the base station canuse the timing information to transmit CSI-RSs in a symbol that allows,in some cases, the UE to calculate channel feedback and transmit thechannel feedback in the same slot in which CSI-RSs are transmitted fromthe base station.

Certain aspects of the present disclosure provide a method for wirelesscommunication that may be performed, for example, by a user equipment(UE). The method generally includes receiving, from a base station (BS),a request for channel feedback identifying a type of channel feedback tobe provided to the BS and a type of channel state information (CSI)reference symbol (RS) (CSI-RS) to be used for generating the identifiedtype of channel feedback, transmitting, to the BS, an indication of anamount of time used to generate the identified type of feedback based onthe identified type of CSI-RS, receiving, from the BS, a triggeringsignal indicating at least a location of one or more CSI-RSs and a timeat which the UE is to report the identified type of channel feedback,wherein the time at which the UE is to report the identified type ofchannel feedback is based, at least in part, on the indicated amount oftime used to generate the identified type of channel feedback andwherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the indicatedlocation of the one or more CSI-RSs, receiving the one or more CSI-RSsin the indicated location, generating the identified type of feedbackbased on the one or more CSI-RSs, and transmitting the generatedfeedback to the BS.

Certain aspects of the present disclosure provide another method forwireless communication that may be performed, for example, by a basestation (BS) (e.g., an eNodeB, a gNodeB, etc.). The method generallyincludes transmitting, to a user equipment (UE), a request for channelfeedback identifying a type of channel feedback to be provided to the BSand a type of channel state information (CSI) reference symbol (RS)(CSI-RS) to be used for generating the identified type of channelfeedback, receiving, from the UE, an indication of an amount of timeused to generate the identified type of feedback based on the identifiedtype of CSI-RS, determining a location in which one or more channelstate information (CSI) reference symbols (RS) (CSI-RSs) are to betransmitted to the UE based on the indicated amount of time,transmitting, to the UE, a triggering signal indicating the determinedlocation of the one or more CSI-RSs and a time at which the UE is toreport the identified type of channel feedback, wherein the time atwhich the UE is to report the identified type of channel feedback isbased, at least in part, on the indicated amount of time used togenerate the identified type of channel feedback and wherein the time atwhich the UE is to report the identified type of channel feedback islater than a time corresponding to the determined location of the one ormore CSI-RSs, transmitting, to the UE, the one or more CSI-RSs in thedetermined location, and receiving, from the UE, the identified type offeedback.

Aspects generally include methods, apparatus, systems, computer readablemediums, and processing systems, as substantially described herein withreference to and as illustrated by the accompanying drawings.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram illustrating an example logical architectureof a distributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 3 is a diagram illustrating example physical architecture of adistributed RAN, in accordance with certain aspects of the presentdisclosure.

FIG. 4 is a block diagram conceptually illustrating a design of anexample BS and user equipment (UE), in accordance with certain aspectsof the present disclosure.

FIG. 5 is a diagram showing examples for implementing a communicationprotocol stack, in accordance with certain aspects of the presentdisclosure.

FIG. 6 illustrates an example of a DL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 7 illustrates an example of an UL-centric subframe, in accordancewith certain aspects of the present disclosure.

FIG. 8 illustrates an example slot diagram illustrating transmission ofchannel state information reference symbols (CSI-RSs) from a basestation and corresponding channel feedback from a UE, in accordance withcertain aspects of the present disclosure.

FIG. 9 is a flow diagram illustrating example operations that may beperformed by a UE for providing channel feedback to a base station (BS)calculated from CSI-RSs transmitted to the UE based on an amount of timeused to generate the channel feedback, in accordance with certainaspects of the present disclosure.

FIG. 10 is a flow diagram illustrating example operations that may beperformed by base station (BS) (e.g., an eNodeB or gNodeB) for receivingchannel feedback from a UE calculated from CSI-RSs transmitted to the UEbased on an amount of time used to generate the channel feedback, inaccordance with certain aspects of the present disclosure.

FIG. 11 illustrates an example slot diagram illustrating transmission ofzero power CSI-RSs (ZP CSI-RSs) and non-zero power CSI-RSs (NZP CSI-RSs)to a UE for generating channel feedback, in accordance with certainaspects of the present disclosure.

FIG. 12 illustrates an example slot diagram illustrating transmission ofCSI-RSs to a UE for generation of channel feedback, in accordance withcertain aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for new radio (NR) (new radioaccess technology or 5G technology). NR may support various wirelesscommunication services, such as Enhanced mobile broadband (eMBB)targeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW)targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC)targeting non-backward compatible MTC techniques, and/or missioncritical targeting ultra reliable low latency communications (URLLC).These services may include latency and reliability requirements. Theseservices may also have different transmission time intervals (TTI) tomeet respective quality of service (QoS) requirements. In addition,these services may co-exist in the same subframe.

In certain systems, (e.g., Release-13 long term evolution (LTE)),enhanced machine type communications (eMTC) are supported, targeting lowcost devices, often at the cost of lower throughput. eMTC may involvehalf duplex (HD) operation in which uplink transmissions and downlinktransmissions can both be performed, but not simultaneously. eMTCdevices, such MTC UEs may look at (e.g., be configured with or monitor)no more than around 1 MHz or six resource blocks (RBs) of bandwidth atany given time. eMTC UEs may be configured to receive no more thanaround 1000 bits per subframe. For example, these eMTC UEs may support amax throughput of around 300 per second. This throughput may besufficient for certain eMTC use cases, such as certain activitytracking, smart meter tracking and/or updates, etc., which may consistof infrequent transmissions of small amounts of data; however, greaterthroughput for eMTC devices may be desirable for other cases, such ascertain Internet-of-Things (IoT) use cases, smart watches, etc.

The following description provides examples, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in some other examples. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim. The word “exemplary”is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

The techniques described herein may be used for various wirelesscommunication networks such as LTE, CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (LIMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Hash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). NRis an emerging wireless communications technology under development inconjunction with the 5G Technology Forum (5GTF). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are releases of UMTS that useE-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, while aspects may be describedherein using terminology commonly associated with 3G and/or 4G wirelesstechnologies, aspects of the present disclosure can be applied in othergeneration-based communication systems, such as 5G and later, includingNR technologies.

Example Wireless Communications System

FIG. 1 illustrates an example wireless network 100 in which aspects ofthe present disclosure may be performed. For example, the wirelessnetwork may be a new radio (NR) or 5G network. UE 120 may be configuredfor enhanced machine type communications (eMTC). The UE 120 may beconsidered a low cost device, low cost UE, eMTC device, and/or eMTC UE.The UE 120 can be configured to support higher bandwidth and/or datarates. For example, the UE 120 may be configured with a plurality ofnarrowband regions (e.g., 24 resource blocks (RBs) or 96 RBs). The UE120 may receive a resource allocation, from a BS 110, allocatingfrequency hopped resources within a system bandwidth, wherein theresource allocation indicates at least one of: non-contiguous narrowbandfrequency resources for uplink transmission in at least one subframe orfrequency resources are not contained within a bandwidth capability ofthe UE to monitor for downlink transmission. The UE 120 may determine,based on the resource allocation, different narrowband frequencyresources for at least one of: uplink transmission in the at least onesubframe or for monitoring for downlink transmission in the at least onesubframe.

As illustrated in FIG. 1, the wireless network 100 may include a numberof BSs 110 and other network entities. A BS may be a station thatcommunicates with UEs. Each BS 110 may provide communication coveragefor a particular geographic area. In 3GPP, the term “cell” can refer toa coverage area of a Node B and/or a Node B subsystem serving thiscoverage area, depending on the context in which the term is used. In NRsystems, the term “cell” and gNB, Node B, 5G NB, AP, NR, BS, NR BS, orTRP may be interchangeable. In some examples, a cell may not necessarilybe stationary, and the geographic area of the cell may move according tothe location of a mobile base station. In some examples, the basestations may be interconnected to one another and/or to one or moreother base stations or network nodes (not shown) in the wireless network100 through various types of backhaul interfaces such as a directphysical connection, a virtual network, or the like using any suitabletransport network.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a frequencychannel, etc. Each frequency may support a single RAT in a givengeographic area in order to avoid interference between wireless networksof different RATs. In some cases, NR or 5G RAT networks may be deployed.

A BS may provide communication coverage for a macro cell, a pico cell, afemto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). A BS for a macro cell may be referred to as a macro BS. A BS fora pico cell may be referred to as a pico BS. A BS for a femto cell maybe referred to as a femto BS or a home BS. In the example shown in FIG.1, the BSs 110 a, 110 b and 110 c may be macro BSs for the macro cells102 a, 102 b and 102 c, respectively. The BS 110 x may be a pico BS fora pico cell 102 x. The BSs 110 y and 110 z may be femto BS for the femtocells 102 y and 102 z, respectively. A BS may support one or multiple(e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., a BS or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or a BS). A relay station may also be a UP, thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with the BS 110 a and a UE 120 r inorder to facilitate communication between the BS 110 a and the UE 120 r.A relay station may also be referred to as a relay BS, a relay, etc.

The wireless network 100 may be a heterogeneous network that includesBSs of different types, e.g., macro BS, pico BS, femto BS, relays, etc.These different types of BSs may have different transmit power levels,different coverage areas, and different impact on interference in thewireless network 100. For example, a macro BS may have a high transmitpower level (e.g., 20 Watts) whereas pico BS, femto BS, and relays mayhave a lower transmit power level (e.g., 1 Watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the BSs may have similar frametiming, and transmissions from different BSs may be approximatelyaligned in time. For asynchronous operation, the BSs may have differentframe timing, and transmissions from different BSs may not be aligned intime. The techniques described herein may be used for both synchronousand asynchronous operation.

A network controller 130 may couple to a set of BSs and providecoordination and control for these BSs. The network controller 130 maycommunicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughout thewireless network 100, and each UE may be stationary or mobile. A UE mayalso be referred to as a mobile station, a terminal, an access terminal,a subscriber unit, a station, a Customer Premises Equipment (CPE), acellular phone, a smart phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, a medical device or medical equipment, a biometricsensor/device, a wearable device such as a smart watch, smart clothing,smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, asmart bracelet, etc.), an entertainment device (e.g., a music device, avideo device, a satellite radio, etc.), a vehicular component or sensor,a smart meter/sensor, industrial manufacturing equipment, a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless or wired medium. Some UEs maybe considered evolved or machine-type communication. (MTC) devices orevolved MTC (eMTC) devices. MTC and eMTC UEs include, for example,robots, drones, remote devices, sensors, meters, monitors, locationtags, etc., that may communicate with a BS, another device (e.g., remotedevice), or some other entity. A wireless node may provide, for example,connectivity for or to a network (e.g., a wide area network such asInternet or a cellular network) via a wired or wireless communicationlink. Some UEs may be considered Internet-of-Things (IoT) devices.

In FIG. 1, a solid line with double arrows indicates desiredtransmissions between a UE and a serving BS, which is a BS designated toserve the UE on the downlink and/or uplink. A finely dashed line withdouble arrows indicates interfering transmissions between a UE and a BS.

Certain wireless networks (e.g., LTE) utilize orthogonal frequencydivision multiplexing (OFDM) on the downlink and single-carrierfrequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDMpartition the system bandwidth into multiple (K) orthogonal subcarriers,which are also commonly referred to as tones, bins, etc. Each subcarriermay be modulated with data. In general, modulation symbols are sent inthe frequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. Forexample, the spacing of the subcarriers may be 15 kHz and the minimumresource allocation (called a ‘resource block’) may be 12 subcarriers(or 180 kHz). Consequently, the nominal FFT size may be equal to 128,256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz(i.e., 6 resource blocks), and there may be 1, 2, 4, 8 or 16 subbandsfor system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively.

While aspects of the examples described herein may be associated withLTE technologies, aspects of the present disclosure may be applicablewith other wireless communications systems, such as NR.

NR may utilize OFDM with a CP on the uplink and downlink and includesupport for half-duplex operation using TDD. A single component carrierbandwidth of 100 MHz may be supported. NR resource blocks may span 12sub-carriers with a sub-carrier bandwidth of 75 kHz over a 0.1 msduration. Each radio frame may consist of 50 subframes with a length of10 ms. Consequently, each subframe may have a length of 0.2 ms. Eachsubframe may indicate a link direction (i.e., DL or UL) for datatransmission and the link direction for each subframe may be dynamicallyswitched. Each subframe may include DL/UL data as well as DL/UL controldata. UL and DL subframes for NR may be as described in more detailbelow with respect to FIGS. 6 and 7. Beamforming may be supported andbeam direction may be dynamically configured. MIMO transmissions withprecoding may also be supported. MIMO configurations in the DL maysupport up to 8 transmit antennas with multi-layer DL transmissions upto 8 streams and up to 2 streams per UE. Multi-layer transmissions withup to 2 streams per UE may be supported. Aggregation of multiple cellsmay be supported with up to 8 serving cells. Alternatively, NR maysupport a different air interface, other than an OFDM-based. NR networksmay include entities such CUs and/or DUs.

In some examples, access to the air interface may be scheduled, whereina scheduling entity (e.g., a base station) allocates resources forcommunication among some or all devices and equipment within its servicearea or cell. Within the present disclosure, as discussed further below,the scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. Base stations arenot the only entities that may function as a scheduling entity. That is,in some examples, a UE may function as a scheduling entity, schedulingresources for one or more subordinate entities (e.g., one or more otherUEs). In this example, the UE is functioning as a scheduling entity, andother UEs utilize resources scheduled by the UE for wirelesscommunication. A UE may function as a scheduling entity in apeer-to-peer (P2P) network, and/or in a mesh network. In a mesh networkexample, UEs may optionally communicate directly with one another inaddition to communicating with the scheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

As noted above, a RAN may include a CU and DUs. A NR BS (e.g., gNB, 5GNB, NB, TRP, AP) may correspond to one or multiple BSs. NR cells can beconfigured as access cells (ACells) or data only cells (DCells). Forexample, the RAN (e.g., a central unit or distributed unit) canconfigure the cells. DCells may be cells used for carrier aggregation ordual connectivity, but not used for initial access, cellselection/reselection, or handover. In some cases DCells may nottransmit synchronization signals in some case cases DCells may transmitSS. NR BSs may transmit downlink signals to UEs indicating the celltype. Based on the cell type indication, the UE may communicate with theNR BS. For example, the UE may determine NR BSs to consider for cellselection, access, handover, and/or measurement based on the indicatedcell type.

FIG. 2 illustrates an example logical architecture of a distributedradio access network (RAN) 200, which may be implemented in the wirelesscommunication system illustrated in FIG. 1. A 5G access node 206 mayinclude an access node controller (ANC) 202. The ANC may be a centralunit (CU) of the distributed RAN 200. The backhaul interface to the nextgeneration core network (NG-CN) 204 may terminate at the ANC. Thebackhaul interface to neighboring next generation access nodes (NG-ANs)may terminate at the ANC. The ANC may include one or more TRPS 208(which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs, orsome other term). As described above, a TRP may be used interchangeablywith “cell.”

The TRPs 208 may be a DU. The TRPs may be connected to one ANC (ANC 202)or more than one ANC (not illustrated). For example, for RAN sharing,radio as a service (RaaS), and service specific AND deployments, the TRPmay be connected to more than one ANC. A TRP may include one or moreantenna ports. The TRPs may be configured to individually (e.g., dynamicselection) or jointly (e.g., joint transmission) serve traffic to a UE.

The local architecture 200 may be used to illustrate fronthauldefinition. The architecture may be defined that support fronthaulingsolutions across different deployment types. For example, thearchitecture may be based on transmit network capabilities (e.g.,bandwidth, latency, and/or jitter).

The architecture may share features and/or components with LTE.According to aspects, the next generation AN (NO-AN) 210 may supportdual connectivity with NR. The NG-AN may share a common front haul forLTE and NR.

The architecture may enable cooperation between and among TRPs 208. Forexample, cooperation may be preset within a TRY and/or across TRPs viathe ANC 202. According to aspects, no inter-TRP interface may beused/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture 200. As will be described in moredetail with reference to FIG. 5, the Radio Resource Control (RRC) layer,Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC)layer, Medium Access Control (MAC) layer, and a Physical (PHY) layersmay be adaptably placed at the DU or CU (e.g., TRP or ANC,respectively). According to certain aspects, a BS may include a centralunit (CU) (e.g., ANC 202) and/or one or more distributed units (e.g.,one or more TRPs 208).

FIG. 3 illustrates an example physical architecture of a distributed RAN300, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 302 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU) 304 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge.

A DU 306 may host one or more TRPs (edge node (EN), an edge unit (EU), aradio head (REI), a smart radio head (SRH), or the like). The DU may belocated at edges of the network with radio frequency (RE) functionality.

FIG. 4 illustrates example components of the BS 110 and UE 120illustrated in FIG. 1, which may be used to implement aspects of thepresent disclosure. One or more components of the BS 110 and UE 120 maybe used to practice aspects of the present disclosure. For example,antennas 452, Tx/Rx 222, processors 466, 458, 464, and/orcontroller/processor 480 of the UE 120 and/or antennas 434, processors460, 420, 438, and/or controller/processor 440 of the BS 110 may be usedto perform the operations described herein and illustrated withreference to FIGS. 10 and 11.

FIG. 4 shows a block diagram of a design of a BS 110 and a UE 120, whichmay be one of the BSs and one of the UEs in FIG. 1. For a restrictedassociation scenario, the base station 110 may be the macro BS 110 c inFIG. 1, and the UE 120 may be the UE 120 y. The base station 110 mayalso be a base station of some other type. The base station 110 may beequipped with antennas 434 a through 434 t, and the UE 120 may beequipped with antennas 452 a through 452 r.

At the base station 110, a transmit processor 420 may receive data froma data source 412 and control information from a controller/processor440. The control information may be for the Physical Broadcast Channel(PBCH), Physical Control Format Indicator Channel (PCFICH), PhysicalHybrid ARQ Indicator Channel (PHICH), Physical Downlink Control Channel(PDCCH), etc. The data may be for the Physical Downlink Shared Channel(PDSCH), etc. The processor 420 may process (e.g., encode and symbolmap) the data and control information to obtain data symbols and controlsymbols, respectively. The processor 420 may also generate referencesymbols, e.g., for the PSS, SSS, and cell-specific reference signal. Atransmit (TX) multiple-input multiple-output (MIMO) processor 430 mayperform spatial processing (e.g., precoding) on the data symbols, thecontrol symbols, and/or the reference symbols, if applicable, and mayprovide output symbol streams to the modulators (MODs) 432 a through 432t. Each modulator 432 may process a respective output symbol stream(e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator432 may further process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal.Downlink signals from modulators 432 a through 432 t may be transmittedvia the antennas 434 a through 434 t, respectively.

At the UE 120, the antennas 452 a through 452 r may receive the downlinksignals from the base station 110 and may provide received signals tothe demodulators (DEMODs) 454 a through 454 r, respectively. Eachdemodulator 454 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 454 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 456 may obtainreceived symbols from all the demodulators 454 a through 454 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 458 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 460, and provide decoded control informationto a controller/processor 480.

On the uplink, at the UE 120, a transmit processor 464 may receive andprocess data (e.g., for the Physical Uplink Shared Channel (PUSCH)) froma data source 462 and control information (e.g., for the Physical UplinkControl Channel (PUCCH) from the controller/processor 480. The transmitprocessor 464 may also generate reference symbols for a referencesignal. The symbols from the transmit processor 464 may be precoded by aTX MIMO processor 466 if applicable, further processed by thedemodulators 454 a through 454 r (e.g., for SC-FDM, etc.), andtransmitted to the base station 110. At the BS 110, the uplink signalsfrom the UE 120 may be received by the antennas 434, processed by themodulators 432, detected by a MIMO detector 436 if applicable, andfurther processed by a receive processor 438 to obtain decoded data andcontrol information sent by the UE 120. The receive processor 438 mayprovide the decoded data to a data sink 439 and the decoded controlinformation to the controller/processor 440.

The controllers/processors 440 and 480 may direct the operation at thebase station 110 and the UE 120, respectively. The processor 440 and/orother processors and modules at the base station 110 may perform ordirect, e.g., the execution of various processes for the techniquesdescribed herein. The processor 480 and/or other processors and modulesat the UE 120 may also perform or direct, e.g., the execution of thefunctional blocks illustrated in FIG. 9, and/or other processes for thetechniques described herein. The processor 440 and/or other processorsand modules at the BS 110 may also perform or direct, e.g., theexecution of the functional blocks illustrated in FIG. 11, and/or otherprocesses for the techniques described herein. The memories 442 and 482may store data and program codes for the BS 110 and the UE 120,respectively. A scheduler 444 may schedule UEs for data transmission onthe downlink and/or uplink.

FIG. 5 illustrates a diagram 500 showing examples for implementing acommunications protocol stack, according to aspects of the presentdisclosure. The illustrated communications protocol stacks may beimplemented by devices operating in a 5G system (e.g., a system thatsupports uplink-based mobility). Diagram 500 illustrates acommunications protocol stack including a Radio Resource Control (RRC)layer 510, a Packet Data Convergence Protocol (PDCP) layer 515, a RadioLink Control (RLC) layer 520, a Medium Access Control (MAC) layer 525,and a Physical (PHY) layer 530. In various examples the layers of aprotocol stack may be implemented as separate modules of software,portions of a processor or ASIC, portions of non-collocated devicesconnected by a communications link, or various combinations thereof.Collocated and non-collocated implementations may be used, for example,in a protocol stack for a network access device (e.g., ANs, CUs, and/orDUs) or a UE.

A first option 505-a shows a split implementation of a protocol stack,in which implementation of the protocol stack is split between acentralized network access device (e.g., an ANC 202 in FIG. 2) anddistributed network access device (e.g., DU 208 in FIG. 2). In the firstoption 505-a, an RRC layer 510 and a PDCP layer 515 may be implementedby the central unit, and an RLC layer 520, a MAC layer 525, and a PHYlayer 530 may be implemented by the DU. In various examples the CU andthe DU may be collocated or non-collocated. The first option 505-a maybe useful in a macro cell, micro cell, or pico cell deployment.

A second option 505-b shows a unified implementation of a protocolstack, in which the protocol stack is implemented in a single networkaccess device (e.g., access node (AN), new radio base station (NR BS), anew radio Node-B (NR NB), a network node (NN), or the like.). In thesecond option, the RRC layer 510, the PDCP layer 515, the RLC layer 520,the MAC layer 525, and the PHY layer 530 may each be implemented by theAN. The second option 505-b may be useful in a femto cell deployment.

Regardless of whether a network access device implements part or all ofa protocol stack, a LIE may implement an entire protocol stack (e.g.,the RRC layer 510, the PDCP layer 515, the RLC layer 520, the MAC layer525, and the PHY layer 530).

FIG. 6 is a diagram 600 showing an example of a DL-centric subframe. TheDL-centric subframe may include a control portion 602. The controlportion 602 may exist in the initial or beginning portion of theDL-centric subframe. The control portion 602 may include variousscheduling information and/or control information corresponding tovarious portions of the DL-centric subframe. In some configurations, thecontrol portion 602 may be a physical DL control channel (PDCCH), asindicated in FIG. 6. The DL-centric subframe may also include a DL dataportion 604. The DL data portion 604 may sometimes be referred to as thepayload of the DL-centric subframe. The DL data portion 604 may includethe communication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion. 604 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 606. Thecommon UL portion 606 may sometimes be referred to as an UL burst, acommon UL burst, and/or various other suitable terms. The common ULportion 606 may include feedback information corresponding to variousother portions of the DL-centric subframe. For example, the common ULportion 606 may include feedback information corresponding to thecontrol portion 602. Non-limiting examples of feedback information mayinclude an ACK signal, a NACK signal, a HARQ indicator, and/or variousother suitable types of information. The common UL portion 606 mayinclude additional or alternative information, such as informationpertaining to random access channel (RACH) procedures, schedulingrequests (SRs), and various other suitable types of information. Asillustrated in FIG. 6, the end of the DL data portion. 604 may beseparated in time from the beginning of the common UL portion 606. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL, communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric subframe and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 7 is a diagram 700 showing an example of an UL-centric subframe.The UL-centric subframe may include a control portion 702. The controlportion 702 may exist in the initial or beginning portion of theUL-centric subframe. The control portion 702 in FIG. 7 may be similar tothe control portion described above with reference to FIG. 6. TheUL-centric subframe may also include an UL data portion 704. The UL dataportion 704 may sometimes be referred to as the payload of theUL-centric subframe. The UL portion may refer to the communicationresources utilized to communicate UL data from the subordinate entity(e.g., UE) to the scheduling entity (e.g., UE or BS). In someconfigurations, the control portion 702 may be a physical DL controlchannel (PDCCH).

As illustrated in FIG. 7, the end of the control portion 702 may beseparated in time from the beginning of the UL data portion 704. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric subframe may alsoinclude a common UL portion 706. The common UL portion 706 in FIG. 7 maybe similar to the common UL portion 706 described above with referenceto FIG. 7. The common UL portion 706 may additional or alternativeinclude information pertaining to channel quality indicator (CQI),sounding reference signals (SRSs), and various other suitable types ofinformation. One of ordinary skill in the art will understand that theforegoing is merely one example of an UL-centric subframe andalternative structures having similar features may exist withoutnecessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet-of-Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

A UE may operate in various radio resource configurations, including aconfiguration associated with transmitting pilots using a dedicated setof resources (e.g., a radio resource control (RRC) dedicated state,etc.) or a configuration associated with transmitting pilots using acommon set of resources (e.g., an RRC common state, etc.). Whenoperating in the RRC dedicated state, the UE may select a dedicated setof resources for transmitting a pilot signal to a network. Whenoperating in the RRC common state, the UE may select a common set ofresources for transmitting a pilot signal to the network. In eithercase, a pilot signal transmitted by the UE may be received by one ormore network access devices, such as an AN, or a DU, or portionsthereof. Each receiving network access device may be configured toreceive and measure pilot signals transmitted on the common set ofresources, and also receive and measure pilot signals transmitted ondedicated sets of resources allocated to the UEs for which the networkaccess device is a member of a monitoring set of network access devicesfor the UE. One or more of the receiving network access devices, or a CUto which receiving network access device(s) transmit the measurements ofthe pilot signals, may use the measurements to identify serving cellsfor the UEs, or to initiate a change of serving cell for one or more ofthe UEs.

Example Coupling of Aperiodic Channel State Information (CSI) ReferenceSymbol (RS) (CSI-RS) Structure with Channel Feedback Content andReporting Timing

Aspects of the present disclosure provide techniques for coupling astructure in which aperiodic CSI-RSs are transmitted to a UE with thecontent of a channel feedback report and timing of the channel feedbackreport. By coupling an aperiodic CSI-RS structure with the content andtiming of a channel feedback report, a base station (BS) can transmitCSI-RSs to a UE in a position within a slot such that the UE cancalculate channel feedback and transmit the calculated channel feedbackwithin the same slot. Further, the CSI-RSs may be transmitted using aport-multiplexing structure that reduces an amount of processing neededto calculate channel feedback.

Multiple input, multiple output (MIMO) transmission and receptiontechniques may be used to increase coverage and network capacity inwireless systems. To implement MIMO techniques, transmission/receptionpoints (TRPs) may receive channel state information (CSI) for a numberof ports at the TRP. CSI-RS is a pilot signal sent on the downlink toget channel information used by MIMO. To obtain CSI, the TRP may receiveUE feedback based on downlink channel estimates generated by the UE fromCSI reference symbols (CSI-RSs) transmitted from the TRP. The UEestimates the channel and feeds hack information such as PMI, RI, orCQI.

For New Radio (NR), TRPs may support at least 32 ports spatially,various slot sizes (e.g., 7-symbol and 14-symbol slots), CSI-RS resourcepooling, and a self-contained slot. TRPs may support CSI-RS transmissionon a periodic, semi-static, or aperiodic basis. For aperiodic CSI-RS,CSI-RS transmission may be triggered (often dynamically), for example,via downlink control information (DCI) messages and/or informationcarried in media access control (MAC) control elements. CSI-RS reportingmay be triggered by DCI messages.

In some cases, different CSI reporting timing may be achieved fordifferent CSI content. For example, calculating channel qualityindicator (CQI) or rank indicator (RI) information may be lesscomputationally expensive than calculating a precoding matrix indicator(PMI) or enhanced Type II CSI feedback, as calculating PMI may entailsweeping across a plurality of spatial streams to identify a precodingmatrix for the TRY to use for transmissions to the UE. In some cases,the CSI content to be reported includes CQI and/or RI. CSI-RS reportingthat contains PMI, or type II feedback computations, may happen on afixed time-offset with respect to the CSI-RS transmission. Also, theCSI-RS transmission and CSI reporting may occur in the same slot if theCSI-RS is transmitted early in the slot.

In some cases, at least two types of CSI-RSs may be identified andtransmitted by a base station to a user equipment for use in calculatingfeedback. The different types of CSI-RSs may include zero power CSI-RSs(ZP CSI-RSs) and non-zero-power CSI-RSs. As discussed in further detailbelow, calculating channel feedback from ZP CSI-RSs may be lesscomputationally expensive than calculating channel feedback from NZPCSI-RSs, which may allow a base station to transmit ZP CSI-RSs in alater symbol than NZP CSI-RSs while maintaining a UE capability totransmit channel feedback in a same slot as the slot in which CSI-RSsare transmitted to the UE.

In some cases, the different types of CSI-RSs may include widebandCSI-RSs and sub-band (or partial-band) CSI-RSs. A wideband CSI-RS maycover the whole band in which a UE operates, while sub-band orpartial-band CSI-RSs may cover a portion of the band in which a UEoperates. In some cases, an amount of time used to generate channelfeedback based on a wideband CSI-RS may differ from an amount of timeused to generate channel feedback based on a narrowband CSI-RS. Asdiscussed herein, a base station can transmit different types of CSI-RSsbased on an expected amount of time used by the UE to calculate channelfeedback; for example, wideband CSI-RSs may be transmitted at adifferent time (e.g., in an earlier symbol in a slot) than sub-band orpartial band CSI-RSs to allow the UE to calculate and report channelfeedback in the same slot as that in which CSI-RSs are transmitted tothe UE.

FIG. 8 illustrates an example slot 800 for transmission of CSI-RS fromthe TRP and CSI reporting, according to some embodiments. Asillustrated, CSI-RS may be transmitted from the TRP in a first symbol802 and a second symbol 804. Further, as illustrated, the UE may use anamount of time 806 spanning a number of OFDM symbols in the slot tocalculate CSI from a received CSI-RS. Because the UE may use the amountof time 806 to calculate CSI, the UE can calculate and report CSI inslot 800 if the CSI-RS is received in first symbol 802, but may not beable to calculate and report CSI in slot 800 if the CSI-RS is receivedis received in second symbol 804. In this example, a UE capability maybe referred to as a minimum number of OFDM symbols (or generally time inmicroseconds) that are used as a gap between the CSI-RS transmission andthe CQI/RI reporting.

FIG. 9 illustrates example operations 900 that may be performed by auser equipment (UE) to report CSI to a base station (BS), such as a TRP,according to an aspect of the present disclosure. As illustrated,operations 900 begin at 902, where the UE receives, from a BS, a requestfir channel feedback. The request may identify a type of channelfeedback to be provided to the BS (e.g., that the BS is requesting thatthe UE report CQI, RI, or PMI). The request may further indicate a typeof channel state information (CSI) reference symbol (RS) (CSI-RS) to beused for generating the identified type of channel feedback.

At 904, the UE transmits, to the BS, an indication of an amount of timeused to generate the identified feedback based on the identified type ofCSI-RS. As discussed herein, the UE can indicate the amount of time usedto generate the identified feedback as a number of symbols correspondingto a minimum amount of time the UE uses to generate the identifiedfeedback. The indicated amount of time represents the minimum time gapused between the transmission of the reference signal (e.g., CSI-RS),and the reporting the UE is being asked to perform.

At 906, the UE receives a triggering symbol indicating a location inwhich one or more CSI-RSs will be received and a time at which the UE isto report the identified type of channel feedback. The time at which theUE is to report the identified type of channel feedback may be based, atleast in part, on the indicated amount of time used to generate theidentified type of channel feedback. The time at which the UE is toreport the identified type of channel feedback may be later than a tunecorresponding to the indicated location of the one or more CSI-RSs.

At 908, the UE receives the CSI-RSs in the indicated location. Thelocation may be, for example, a symbol index in which the BS transmitsthe CSI-RSs to the UE. As discussed herein, the location in which theCSI-RSs are received may be based on the indicated amount of time usedto generate the identified feedback.

At 910, the UE generates the identified feedback based on the one ormore CSI-RSs. At 912, the UE transmits the generated feedback to the BS.

FIG. 10 illustrates example operations 1000 that may be performed by aBS to receive CSI from a UE, according to an aspect of the presentdisclosure. As illustrated, operations 1000 begin at 1002, where the BStransmits, to the UE, a request for channel feedback. The request mayidentify a type of channel feedback to be provided to the BS (e.g., thatthe BS is requesting that the UE report CQI, RI, or PMI). The requestmay further indicate a type of channel state information (CSI) referencesymbol (RS) (CSI-RS) to be used for generating the identified type ofchannel feedback.

At 1004, the BS receives, from the UE, an indication of an amount oftime used to generate the identified type of feedback based on theidentified type of channel feedback. The amount of time may be indicatedas a number of symbols between reception of CSI-RSs and the earliesttime at which the UE can transmit the requested feedback to the BS. At1006, based on the indication of an amount of time used for the UE togenerate the identified type of feedback, the BS determines a locationin which one or more CSI-RSs are to be transmitted to the UE.

At 1008, the BS transmits, to the UE, a triggering symbol indicating thedetermined location of the one or more CSI-RSs and a time at which theUE is to report the identified type of channel feedback. The time atwhich the UE is to report the identified type of channel feedback may bebased, at least in part, on the indicated amount of time used togenerate the identified type of channel feedback. The time at which theUE is to report the identified type of channel feedback may be laterthan a time corresponding to the indicated location of the one or moreCSI-RSs.

At 1010, the BS transmits, to the UE, the one or more CSI-RSs in thedetermined location. The location in which the BS transmits the one ormore CSI-RSs may be based, at least in part, on the indicated amount oftime used for the UE to calculate the requested type of channelfeedback. At 1012, the BS receives the identified type of feedback fromthe UE.

In some cases, the generated feedback may be transmitted with a sameslot as the request for channel feedback, which may be referred to as“fast CSI reporting.” When fast CSI reporting is used, CSI-RSs need notbe multiplexed using a time-domain orthogonal cover code (OCC). Byomitting a time-domain OCC, a UE need not receive and buffer all of thesymbols on the ports that are to be estimated before beginning tocalculate channel feedback. When using a OCC, UE will wait to receiveall symbols before starting the CQI computation.

In some cases, CSI-RSs may be transmitted to a UE as zero power (ZP)CSI-RSs or non-zero power (NZP) CSI-RSs. ZP CSI-RSs may be transmittedwith zero power, and a UE can identify interference on the CSI-RSs bydetecting an amount of power received at a time in which ZP CSI-RSs aretransmitted from the BS. Calculating channel feedback based on a ZPCSI-RS may be less computationally expensive than calculating channelfeedback for NZP CSI-RSs. As illustrated by slot diagram 1100 in FIG.11, a UE can calculate channel feedback based on a ZP CSI-RS using atime duration 1102 and can calculate channel feedback based on an NZPCSI-RS using a time duration 1104, which may be a longer time durationthan time duration 1102. Because time duration 1104 may be longer thantime duration 1102, to allow a UE to calculate and report channelfeedback in the same slot in which the UE receives CSI-RSs from a BS,the UE may transmit NLP CSI-RSs in a first symbol that is positionedearlier in a slot than a second symbol in which the BS transmits ZPCSI-RSs to the UE.

In some cases, a UE may be able to calculate and report PMI for alimited number of ports (e.g., two-port PMI or four-port PMI) in thesame slot in which the UE receives a CSI-RS. For example, as illustratedby slot diagram 1200 in FIG. 12, a UE may be able to calculate PMI for alimited number of ports if the UE receives the CSI-RS early in a slot,such as a symbol after a symbol in which a CSI-RS triggering signal iscarried. As illustrated, the CSI-RS triggering signal may be carried insymbol 0, which may be allocated for control information, and the CSI-RSmay be carried in symbol 1. The UE may calculate PMI for a limitednumber of ports, which the UE can indicate to the BS in uplinksignaling, and may report the calculated PMI in the last uplink symbolin the slot (e.g., symbol 13 in the 14-symbol slot illustrated in FIG.12). Thus, the UE, in this example, receives a CSI-RS, calculates PMIfor a limited number of ports, and reports the calculated PMI within thesame slot.

The number of symbols reported by the UE as the minimum number ofsymbols that may elapse between reception of the CSI-RSs andtransmission of channel feedback to the BS may differ based on a slotnumerology. In some cases, the minimum number of symbols need not scalelinearly with the scaling of the subcarrier spacing. For example, in a14-symbol slot with a 30 KHz subcarrier spacing, a slot may have aduration of 0.5 milliseconds, and in an example, the UE may specify a4-symbol gap between receiving CSI-RSs from the BS and transmission ofchannel feedback to the BS. For a 60 KHz subcarrier spacing and a14-symbol slot having a duration of 0.25 milliseconds, the gap betweenreceiving CSI-RSs from the BS and transmission of channel feedback tothe BS within the same slot may comprise any number of symbols (e.g.,need not also linearly scale from 4 symbols to 8 symbols) or may not besupported at all.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PLAY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular applicator and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: receiving, from a base station (BS), arequest for channel feedback identifying a type of channel feedback tobe provided to the BS and a type of channel state information (CSI)reference signal (RS) (CSI-RS) to be used for generating the identifiedtype of channel feedback; transmitting, to the BS, an indication of anamount of time used to generate the identified type of feedback based onthe identified type of CSI-RS; receiving, from the BS, a triggeringsignal indicating at least a location of one or more CSI-RSs and a timeat which the UE is to report the identified type of channel feedback,wherein the time at which the UE is to report the identified type ofchannel feedback is based, at least in part, on the indicated amount oftime used to generate the identified type of channel feedback andwherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the indicatedlocation of the one or more CSI-RSs; receiving the one or more CSI-RSsin the indicated location; generating the identified type of feedbackbased on the one or more CSI-RSs; and transmitting the generatedfeedback to the BS.
 2. The method of claim 1, wherein the type offeedback comprises one of a channel quality indicator (CQI) or a rankindicator (RI).
 3. The method of claim 2, wherein the generated feedbackis transmitted within a same slot as a slot in which the request forchannel feedback and the one or more CSI-RSs is received.
 4. The methodof claim 3, wherein the one or more CSI-RSs received in the indicatedlocation and used for generating the identified type of channel feedbackare received without an orthogonal cover code (OCC).
 5. The method ofclaim 1, wherein the request identifies a second type of CSI-RS to beused for generating the identified type of channel feedback, wherein thetype of CSI-RS comprises a zero-power CSI-RS (ZP CSI-RS) and the secondtype of CSI-RS comprises a non-zero-power CSI-RS (NZP CSI-RS), andwherein the type of CSI-RS is received in later symbols than symbols inwhich the second type of CSI-RS is received.
 6. The method of claim 1,wherein the request identifies a plurality of a second type of CSI-RSsto be used for generating the identified type of channel feedback,wherein the type of CSI-RS comprises a non-zero-power CSI-RS (NZPCSI-RS) and the second type comprises a zero-power CSI-RS (ZP CSI-RS),and wherein the plurality of CSI-RSs of the second type of CSI-RS arereceived in later symbols than a symbol in which the CSI-RS of the firsttype is received.
 7. The method of claim 1, wherein the request forchannel feedback further identifies a plurality of ports for whichchannel feedback is requested.
 8. The method of claim 7, furthercomprising transmitting the channel feedback to the BS in a last uplinksymbol in a slot, wherein the CSI-RSs are received in a symbolsubsequent to a symbol in which the triggering signal is received. 9.The method of claim 7, wherein the type of channel feedback comprisesprecoding matrix indicator (PMI) feedback for the identified pluralityof ports.
 10. The method of claim 1, further comprising: indicating, tothe BS, a maximum number of ports for which the UE can generate feedbackin a same slot as a slot in which the CSI-RSs are received from the BS.11. The method of claim 1, wherein the request is aperiodic.
 12. Themethod of claim 1, wherein the request is carried in a downlink controlinformation (DCI) message or in a media access control (MAC) controlelement (CE).
 13. The method of claim 1, wherein the amount of time usedto generate the identified feedback comprises a number of symbols in aslot, wherein the number of symbols is different for differentsubcarrier spacings.
 14. An apparatus comprising: a processor; and amemory storing instructions for: receiving, from a base station (BS), arequest for channel feedback identifying a type of channel feedback tobe provided to the BS and a type of channel state information (CSI)reference signal (RS) (CSI-RS) to be used for generating the identifiedtype of channel feedback; transmitting, to the BS, an indication of anamount of time used to generate the identified type of feedback based onthe identified type of CSI-RS; receiving, from the BS, a triggeringsignal indicating at least a location of one or more CSI-RSs and a timeat which the UE is to report the identified type of channel feedback,wherein the time at which the UE is to report the identified type ofchannel feedback is based, at least in part, on the indicated amount oftime used to generate the identified type of channel feedback andwherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the indicatedlocation of the one or more CSI-RSs; receiving the one or more CSI-RSsin the indicated location; generating the identified type of feedbackbased on the one or more CSI-RSs; and transmitting the generatedfeedback to the BS.
 15. An apparatus for wireless communications,comprising: means for receiving, from a base station (BS), a request forchannel feedback identifying a type of channel feedback to be providedto the BS and a type of channel state information (CSI) reference signal(RS) (CSI-RS) to be used for generating the identified type of channelfeedback; means for transmitting, to the BS, an indication of an amountof time used to generate the identified type of feedback based on theidentified type of CSI-RS; means for receiving, from the BS, atriggering signal indicating at least a location of one or more CSI-RSsand a time at which the UE is to report the identified type of channelfeedback, wherein the time at which the UE is to report the identifiedtype of channel feedback is based, at least in part, on the indicatedamount of time used to generate the identified type of channel feedbackand wherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the indicatedlocation of the one or more CSI-RSs; means for receiving the one or moreCSI-RSs in the indicated location; means for generating the identifiedtype of feedback based on the one or more CSI-RSs; and means fortransmitting the generated feedback to the BS.
 16. A method for wirelesscommunications by a base station (BS), comprising: transmitting, to auser equipment (UE), a request for channel feedback identifying a typeof channel feedback to be provided to the BS and a type of channel stateinformation (CSI) reference signal (RS) (CSI-RS) to be used forgenerating the identified type of channel feedback; receiving, from theUE, an indication of an amount of time used to generate the identifiedtype of feedback based on the identified type of CSI-RS; determining alocation in which one or more channel state information (CSI) referencesignals (RS) (CSI-RSs) are to be transmitted to the UE based on theindicated amount of time; transmitting, to the UE, a triggering signalindicating the determined location of the one or more CSI-RSs and a timeat which the UE is to report the identified type of channel feedback,wherein the time at which the UE is to report the identified type ofchannel feedback is based, at least in part, on the indicated amount oftime used to generate the identified type of channel feedback andwherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the determinedlocation of the one or more CSI-RSs; transmitting, to the UE, the one ormore CSI-RSs in the determined location; and receiving, from the UE, theidentified type of feedback.
 17. The method of claim 16, wherein thetype of feedback comprises one of a channel quality indicator (CQI) or arank indicator (RI).
 18. The method of claim 17, wherein the feedback isreceived within a same slot as the request for channel feedback and theone or more CSI-RSs.
 19. The method of claim 18, wherein the one or moreCSI-RSs transmitted in the determined location and for use in generatingthe determined type of channel feedback are transmitted without anorthogonal cover code (OCC).
 20. The method of claim 16, wherein therequest identifies a second type of CSI-RS to be used for generating theidentified type of channel feedback, wherein the type of CSI-RScomprises a zero-power CSI-RS (ZP CSI-RS) and the second type of CSI-RScomprises a non-zero-power CSI-RS (NZP CSI-RS), and wherein the type ofCSI-RS is transmitted in later symbols than symbols in which the secondtype of CSI-RS is transmitted.
 21. The method of claim 16, wherein therequest identifies a second type of CSI-RS to be used for generating theidentified type of channel feedback, wherein the type of CSI-RScomprises a non-zero-power CSI-RS (NZP CSI-RS) and the second type ofCSI-RS comprises a zero-power CSI-RS (ZP CSI-RS), and wherein theplurality of CSI-RSs of the second type are transmitted in later symbolsthan a symbol in which the CSI-RS of the first type is transmitted. 22.The method of claim 16, wherein the request for channel feedback furtheridentifies a plurality of ports for which the channel feedback isrequested.
 23. The method of claim 22, wherein the feedback is receivedin a last uplink symbol in a slot, wherein the CSI-RSs are transmittedin a symbol subsequent to a symbol in which the triggering signal istransmitted.
 24. The method of claim 22, wherein the type of channelfeedback comprises precoding matrix indicator (PMI) feedback for theidentified plurality of ports.
 25. The method of claim 16, furthercomprising: receiving, from the UE, an indication of a maximum number ofports for which the UE can generate feedback as a same slot as a slot inwhich the CSI-RSs are transmitted from the BS.
 26. The method of claim16, wherein the request is aperiodic.
 27. The method of claim 16,wherein the request is carried in a downlink control information (DCI)message or in a media access control (MAC) control element (CE).
 28. Themethod of claim 16, wherein the amount of time used to generate theidentified type of feedback comprises a number of symbols in a slot,wherein the number of symbols is different for different subcarrierspacings.
 29. An apparatus for wireless communications, comprising: aprocessor; and a memory storing instructions for: transmitting, to auser equipment (UE), a request for channel feedback identifying a typeof channel feedback to be provided to the BS and a type of channel stateinformation (CSI) reference signal (RS) (CSI-RS) to be used forgenerating the identified type of channel feedback; receiving, from theUE, an indication of an amount of time used to generate the identifiedtype of feedback based on the identified type of CSI-RS; determining alocation in which one or more channel state information (CSI) referencesignals (RS) (CSI-RSs) are to be transmitted to the UE based on theindicated amount of time; transmitting, to the UE, a triggering signalindicating the determined location of the one or more CSI-RSs and a timeat which the UE is to report the identified type of channel feedback,wherein the time at which the UE is to report the identified type ofchannel feedback is based, at least in part, on the indicated amount oftime used to generate the identified type of channel feedback andwherein the time at which the UE is to report the identified type ofchannel feedback is later than a time corresponding to the determinedlocation of the one or more CSI-RSs; transmitting, to the UE, the one ormore CSI-RSs in the determined location; and receiving, from the UE, theidentified type of feedback.
 30. An apparatus for wirelesscommunications, comprising: means for transmitting, to a user equipment(UE), a request for channel feedback identifying a type of channelfeedback to be provided to the BS and a type of channel stateinformation (CSI) reference signal (RS) (CSI-RS) to be used forgenerating the identified type of channel feedback; means for receiving,from the UE, an indication of an amount of time used to generate theidentified type of feedback based on the identified type of CSI-RS;means for determining a location in which one or more channel stateinformation (CSI) reference signals (RS) (CSI-RSs) are to be transmittedto the UE based on the indicated amount of time; means for transmitting,to the UE, a triggering signal indicating the determined location of theone or more CSI-RSs and a time at which the UE is to report theidentified type of channel feedback, wherein the time at which the UE isto report the identified type of channel feedback is based, at least inpart, on the indicated amount of time used to generate the identifiedtype of channel feedback and wherein the time at which the UE is toreport the identified type of channel feedback is later than a timecorresponding to the determined location of the one or more CSI-RSs;means for transmitting, to the UE, the one or more CSI-RSs in thedetermined location; and means for receiving, from the UE, theidentified type of feedback.